1. Field of the Invention
This invention relates to a gyro and, more particularly, it relates to a gyro for detecting the rate and sense rotation by using a ring laser.
2. Related Background Art
Known gyros for detecting the angular velocity of a moving object include mechanical gyros comprising a rotor or an oscillator as well as optical gyros. Particularly, optical gyros are bringing forth technological innovations in the field of gyro technologies due to their remarkable advantages including that they can start to operate instantaneously and have a broad dynamic range.
Various optical gyros are known to date including ring laser type gyros, optical fiber gyros and passive type ring resonator gyros. Of these, the ring laser type gyro that utilizes a gas laser is the earliest comer and gyros of this type are popularly used in aeroplanes at present. In recent years, small and highly sophisticated ring laser type gyros that are integrated on a semiconductor substrate have been proposed. See, inter alia, Japanese Patent Application Laid-Open No. 5-288556, Japanese Patent Publication No. 62-39836 (U.S. Pat. No. 4,431,308) and Japanese Patent Application Laid-Open No. 4-174317.
FIG. 7 of the accompanying drawings illustrates a gyro disclosed in U.S. Pat. No. 4,431,308 that utilizes the change in the terminal voltage of a semiconductor laser device caused by rotation without taking out beams to the outside of the semiconductor laser device. Referring to FIG. 7, a semiconductor laser device 500 has upper and lower electrodes 501, 502. In FIG. 7, reference numeral 503 denotes a DC blocking capacitor and reference numeral 504 denotes an output terminal, while reference numeral 505 denotes a resistor. As seen from FIG. 7, the semiconductor laser device with a ring cavity is connected to a drive power source 506 and the frequency difference (beat frequency) between the frequency of the beam propagating clockwise and that of the beam propagating counterclockwise that is caused when a certain angular velocity is applied to the device is detected as a change in the terminal voltage of the laser device.
As a technique for processing the signal from a laser gyro, the oscillation frequency of the output signal may be converted into a voltage signal by means of a frequency-voltage converting circuit. Such a frequency-voltage converter circuit may be a circuit which processes analog signals or which obtains the output voltage by digitizing analog signals to count the number of pulses or by integrating analog signals for a predetermined period of time.
However, when a frequency-voltage converter circuit is used to detect the angular velocity of a known gyro from the frequency of the obtained beat signal, there arises occasions where it is impossible to know the frequency unless the phase angle of the signal shows at least a shift of 2xcfx80. For instance, when the angular velocity to be observed is about 0.1 deg/sec. and the frequency of the beat signal taken out from the element is about 1 Hz, it takes about 1 second for the shift of the phase angle of the signal to become equal to 2xcfx80. Therefore, a novel device is required to detect an angular vibration change of a gyro used in an anti-vibration system with a response frequency between 1 and 100 Hz. Additionally, there has been a problem that known gyros are not able to detect the sense of rotation.
Therefore, it is an object of the present invention to provide a signal processing system that can detect the angular velocity within a short period of time even when the frequency of the beat signal is low and to provide a gyro comprising such a signal processing system.
Another object of the invention is to provide a gyro that can detect the sense of rotation.
According to the invention, the above objects are achieved by providing a gyro comprising:
a ring-resonator type laser;
a vibration table for applying an oscillation to the laser; and
a signal processing means for processing the output of the laser;
the signal processing means determining the phase angle from the amplitude of an oscillation cycle component of the vibration table and that of a higher harmonic component thereof.
The signal processing means carries out a differential operation on the phase angle to obtain an angular velocity.
The higher harmonic component is a component having a cycle that is twice as long as the oscillation cycle of the vibration table.
The signal processing means operates to obtain the amplitude of the oscillation applied to the vibration table.
Additionally, the present invention is characterized in that the direction of the normal of the resonator of the ring laser agrees with the direction of the axis of rotation of the vibration table.
The present invention is further characterized in that a micro-oscillation having a frequency above the frequency range of the angular velocity signal of an object to be detected is applied to the vibration table.